| In this study, a popular maize cultivar “ZhengDan-958’’ was used as material, with themethod of conventional potted plant experiment at room temperature, and cell biology, plantphysiology, histochemistry and other multi-disciplinary research techniques, based on themetabolism of ROS, the changes of Kranz anatomy and photosynthetic traits and thedistribution of H2O2and K+in guard and subsidiary cells under different water stress (75%~85%of field capacity, CK;65%~75%of field capacity, LS;55%~65of field capacity, MS;45%~55%of field capacity, SS), using the research techniques of spectrophotometer, specifichistochemical staining, semi-thin sectioning, fluorescent microscope and ordinary microscope.We analyzed the effect of the metabolism of ROS on the changes of Kranz anatomy andphotosynthetic traits, and the relationship between H2O2and K+in regulating stomatalmovement, which provided cytological evidence about the effects of ROS on maize and alsopaved the great way for later study on the source of H2O2in subsidiary cells of monocotyledon,the definite function of it on stomatal movement and the similarities and differences of H2O2inguard and subsidiary cells in adjusting K+channels. The results and conclusions were asfollows:(1)The effects of water stress on ROS metabolism: as the increasing of water stress level,O2.-and H2O2produced with a symptom of soaring contents in the seeding leaves of maize,especially under middle and severe stress, them increased heavily. To reduce the damage of cornplants, the antioxidant enzyme system in the leaves also changed. The activitives of peroxidase(POD) increased continuous following the decrease of soil water, reaching the most abundantunder severe stress. The variation tendencies of CAT (H2O2enzyme) and SOD (superoxide dismutase) were consistent. They presented downward trend after rising first, reaching themaximum under middle stress. The above showed that under LS and MS, the antioxidantenzymes were enough to remove the small number of ROS, however, under SS the abundantROS accumulated in the leaves were not removed completely, and the balance of ROSmetabolism disordered aggravatingly, which induced the membrane lipid peroxidation enhanced,mainly reflecting in the gradually increasing content of MDA.(2)The effects of water stress on Kranz anatomy of leaves and photosynthetic traits: as thewater stress level increasing, the normal structure of wreath was damaged, the wreath cellsarranged messy and cell size became smaller and smaller, bundle sheath cells went irregular andthe numbers of chloroplast in this two kinds of cell decreased, the chlorophyll content in themesophyll cell decreased, as well. Compared with the control group, the wreath structure underLS changes little. The chloroplasts in wreath cells became separate from plasma membrane, thatwas, they spread from the innermost inside of cytoplasmic membrane, cling on the cell wall tothe center of the cell approximate under middle stress, which increased the light absorption areaand may be an adaption of the enviroment. The vascular bundle under SS already atrophied andthe wreath structure deformated seriously. The damaged Kranz anatomy ultimately induced thedecrease of Net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance(Cond),intercellular CO2concentration (Ci) reduced after rising because of the reduction of Pn.(3)The distribution of H2O2and K+and the relationshiops between them in regulatingstomatal movement: under normal water condition, there was only little H2O2in guard cells, withthe enhancement of water stress, the H2O2in guard and subsidiary cells were both increasinggradually, and the stomatal closed. The results were the same as the above under PEG simulateddrought stress. However, K+had the different distribution, almost all the K+distributed in guardcell under normal water condition, afterwards, as the water stress increasing, the H2O2in guardcells decreased gradually and increased in subsidiary cells. And that, in the extreme conditions,for example, in light, there was little H2O2distributing in guard cells, none in subsidiary cells,but almost all the K+distributed in guard cells, and the stomas were open. In darkness, a largenumber of H2O2distributed in guard cells and subsidiary cells, but almost all the K+distributedin subsidiary cells, and the stoma were close. When the epidermal tissues were initially keptunder light for4H, and then transferred to the darkness with NADPH oxidase inhibitors DPI(diphenyleneio-donium) and H2O2scavenger DMTU (N,N-dimethyl thiourea) and KI for4H, orput them in darkness for4H, and then transferred them to the natural enviroment with DPI,DMTU and KI for4H, we got the same results, that were, the fluorescence intensity of H2O2inguard cells and subsidiary cells were both reduced, but the distributions didn’t change. However, the K+changed dramaticlly, their distributions changed from almost in subsidiary cells withoutchemicals to guard cells with them and the stomatal aperture were gradually increased, as well.We draw the following conclusion based on the above experiment results: ROS, in additionto destroying the structure of corn leaf, and then, affected the photosynthesis, its one of the moststable substance, H2O2as a kind of signal involved in stomatal movement, as well. Not only didthe H2O2in guard cells have certain leading role in stomatal movement, but also theaccumulation of H2O2in subsidiary cells had the function of adjusting or collaborativing guardcells in stomatal movement. Under different water stress and light and dark, the H2O2both inguard and subsidiary cells regulated the stomatal movement by adjusting the distribution of K+,but they may had different ways in regulating K+channels. DMTU, DPI and KI had certainreversal effects on stomatal closure induced by dark, that was, they inhibited the closure ofstomatal; at the same time, they also promoted stomatal opening. Due to stoma is the channel forthe exchange of moisture and carbon dioxide between plant and the outside world, after theclosure of stomatal induced by H2O2, the process was then blocked, which also had a certaininfluences on photosynthesis. |
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